A survey on object deformation and decomposition in computer graphics

Highlights

• We present a state of the art report on object deformation and decomposition.

• We examine natural phenomena that lead to major object morphology changes.

• The focus is on effects which influence the structure and geometry of the object.

• The methods are categorised according to the phenomena that drive the deformation.

• We pay particular attention to object representation and deformation techniques.

Abstract

In a realistic world, objects are expected to change in appearance over time when exposed to their environment. Morphology changes can be important indicators of an object׳s make up and the environment in which it exists. Simulating changes in an object׳s appearance over time has become increasingly popular over the recent years. In this survey we will describe a number of methods used in computer graphics to simulate object morphology changes due natural influences, such as cracks, fractures, patina, corrosion, erosion, burning, melting, decay, rotting and withering. We will focus on approaches that consider effects which influence the geometry of the entire object, instead of the surface appearance alone. The methods described are categorised according to the natural phenomena that drive the appearance changes. We pay particular attention to the different object representation and deformation techniques used in current approaches. The aim of this article is to provide a comprehensive overview of the state of the art in the area of object morphology changes driven by the environment.

Introduction

Real world objects are not immutable and free of blemishes, but tend to change in appearance over time when exposed to their environment. As such, simulating these phenomena can have a significant impact on the perceived realism of a computer generated scene. Artists can manually compose and manipulate different textures and models which illustrate the different stages of objects under alteration. However, this can be a very labour-intensive and time-consuming process. An artist may have to create textures and different models for every object under different environmental settings. An alternative approach is to automate the generation and modification of textures and models in order to achieve the desired effects. Currently researchers in the area have developed a number of different approaches to model a variety of natural influences on virtual objects.

While methods to simulate erosion have been present for some time [1], [2], other processes such as decay of organic objects are still emerging and evolving. [3] offer an overview of weathering and ageing phenomena in computer graphics, however, the methods described mainly focus on surface changes, such as texture generation, BRDF and colouration changes and do not consider rotting and withering of organic objects. There are several papers that focus on general deformable models in computer graphics [4], [5], but they do not consider the phenomena that cause the deformation.

Our aim is to give an overview of the state of the art in the area of object morphology changes due to the influence of the environment. In contrast to [3], [4], [5], the focus of this survey is the natural phenomena which lead to structural and morphological changes. We only consider the environmental processes that deteriorate objects over time. Phenomena that do not lead to the decline of an object, such as wetting, are not considered in this survey. Furthermore, we focus on methods that consider geometrical and structural changes, such as fracturing, deformations and holes and omit those that only affect the object׳s shading and surface (such as staining, dust, and tarnishing). Natural phenomena that satisfy these criteria include weathering and ageing effects, such as corrosion, rotting, erosion and other phenomena such as burning and melting.

The changes an object undergoes depend on the natural phenomena involved and as such we categorise the different methods according to the physical process behind the deformation. Aside from the methods used to simulate the phenomena themselves, we will look at the techniques used to model and deform the affected object. Objects, such as fruit and rocks, tend to consist of heterogeneous material or are made of different layers which affect their appearance and degeneration. We will discuss how representative a chosen model is of its real world counterpart and to what degree this affects the simulation results. The deformation techniques will be evaluated according to their level of effect on the object, i.e. whether they affect the surface geometry, the thin shell geometry or the whole volume. To the best of the authors׳ knowledge there is currently no other published survey that concentrates on the different natural phenomena that lead to major geometric deformations of an object.